Symposium G
Multifunctional Inorganic One-dimensional Nanostructures: Status and Potential


Session G-1 - Growth and Functionalization of 1-D Nanostructure

G-1:IL01  Controlled Growth and Optoelectronic Properties of Wide Bandgap Semiconducting Nanowires
S. GRADECAK, Department of Materials Science and Engineering, MIT, Cambridge, MA, USA

Nanowires offer solutions to some of the current challenges in science and engineering, but realization of their full potential will be ultimately dictated by the ability to control their structure, composition, and size with high accuracy. In this talk, I will discuss our recent results on the controlled growth, doping, and applications of wide bandgap nanowires, as well as advanced electron microscopy techniques for direct correlation of structural and physical properties with high spatial resolution. We have developed a simple, yet powerful, approach to modulate both the diameter and composition of individual III-V nitride nanowires by adjusting in-situ the nanowire seed particle composition and volume. In addition, we demonstrate independent tailoring of the hydrothermally grown zinc oxide (ZnO) nanowire dimensions including areal density, length, and diameter. We have demonstrated that the cathodoluminescence (CL) technique, coupled with scanning transmission electron microscopy (STEM), effectively bypasses the resolution limit of conventional far-field photoluminescence spectroscopy and allows direct structure-property correlation on the nanoscale. Finally, applications of semiconductor nanowires for LED and solar cell applications will be described.

G-1:IL02  Growth and Structure of Self-catalyzed III-V Nanowires on Silicon 
V.G. DUBROVSKII, St. Petersburg Academic University, St. Petersburg, Russia Ioffe Physical Technical Institute RAS, St. Petersburg, Russia

Self-catalyzed III-V nanowires offer an ideal platform for III-V optoelectronic devices on silicon substrates. The use of Ga droplets to facilitate the vapor-liquid-solid (VLS) growth of GaAs nanowires has been proven efficient from several perspectives. First, one can use well-developed methods for processing SiOx layers to prepare Ga droplet arrays. Second, the Ga-assisted growth allows for elimination of unwanted Au contamination. Third, the crystal structure of these GaAs nanowires appears to be predominantly zincblende. Fourth, the liquid alloy during the self-catalyzed growth is binary Ga-As rather than ternary Au-Ga-As and the elongation rate is determined entirely by the kinetics of As species. Recently, the self-catalyzed approach has demonstrated its potential for fabrication of complex structures with variable dimensions. Some of the new results are considered in more detail in this talk. In particular, I will demonstrate that Ga-catalyzed VLS growth can be stopped and resumed at will to produce high quality nanowires with modulated diameter. I will also discuss an interesting effect of radius self-equilibration which helps to fabricate regular ensembles of GaAs nanowires and is specific to self-catalyzed VLS growth.

G-1:IL03  GaN/InGaN Nanowire Structures - MBE Growth and Optical Properties
H. RIECHERT, Paul-Drude-Institut, Berlin, Germany

In this talk I will review the present understanding of the MBE growth of GaN nanowires on Si in a catalyst-free approach. A comprehensive model for both, nucleation and subsequent growth will be presented. Using in-situ quadrupole mass spectroscopy, excellent control over the growth is provided. This includes a post-growth annealing step which can controllaby reduce nanowire diameters to the range where we obtain true 1D nanostructures. By employing high growth temperatures, we obtain excellent optical properties which approach those of free-standing bulk GaN. The presented results build on the work of many coworkers at PDI, whose contributions will be indicated during the talk.

G-1:IL04  Demonstration of Hole Gas Accumulation Control in Ge/Si Core-shell Nanowires
NAOKI FUKATA1, K. NISHIBE1, M. YU1, W. JEVASUWAN1, T. TAKEI1, Y. BANDO1, W. WU2, Z.L. WANG2, 1National Institute for Materials Science (NIMS), Tsukuba, Japan; 2School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA, USA

Silicon and germanium nanowires (SiNWs and GeNWs) are anticipated for the realization of next-generation metal-oxide-semiconductor field-effect transistors and solar cells. Impurity doping is one of the key techniques for the NWs devices, while the retardation of carrier mobility due to impurity scattering has to be taken into account. Core-shell NWs composed of Si and Ge are key structures for realizing high mobility transistor channels, since core-shell structures separate the carrier transport region from the impurity doped region, resulting in the suppression of impurity scattering. Ge/Si core-shell NWs structures were rationally grown on a Si substrate by CVD. Selective doping and band-offset in Ge/ Si core-shell NW structures can realize a type of high electron mobility transistor (HEMT) structure in one-dimensional NWs by separating the carrier transport region from the impurity-doped region. Precise analysis, using Raman spectroscopy of the Ge optical phonon peak, can distinguish three effects: the phonon confinement effect, the stress effect due to the heterostructures, and the Fano effect. Using these techniques, we obtained conclusive evidence of hole gas accumulation in Ge/Si core-shell NWs. The control of hole gas concentration can be realized by changing the B doping concentration in the Si shell.

G-1:IL05  Heterostructure Formation in Nanowires of Alloyed Compound Semiconductors - Experiments and Theory
F. GLAS, G. PRIANTE, F. OEHLER, K. PANTZAS, G. PATRIARCHE, J.-C. HARMAND, Laboratoire de Photonique et de Nanostructures, CNRS, Université Paris Saclay, Marcoussis, France

In principle, semiconductor nanowires (NWs) allow one to control precisely the geometry and composition of nanostructures, e.g. by growing an axial insertion on top of a NW stem. However, in vapor-liquid-solid growth, the reservoir effect (accumulation of NW constituents in the apical droplet) may hinder the formation of sharp interfaces. We studied experimentally and theoretically the formation of axial heterostructures in III-V NWs. Experimentally, we concentrate on two systems grown in the self-catalyzed mode by molecular beam epitaxy, namely Ga(P,As) and (Al,Ga)As, where the interfaces involve alternations (or concentration changes) of atoms of groups V and III, respectively. Using composition measurements carried out by transmission electron microscopy with monolayer resolution, we discuss how the reservoir effect affects the abruptness of these interfaces and assess growth procedures that we devised to circumvent it. Based on the thermodynamics of the III-V ternary alloys, we develop a kinetic model that describes quantitatively the composition profiles across such interfaces. Our ultimate aim being to control the thickness of axial insertions at the monolayer level, we discuss how the interplay of nucleation statistics and kinetics affects the formation of such insertions.

G-1:IL06  Hybrid Nanophotonics-nanomaterial Platforms with III/V Semiconductor Nanowires on Si
MASAYA NOTOMI, NTT Basic Research Laboratories and NTT Nano-photonics Center, Atsugi, Japan

Recently, various nano-scale functional materials are extensively studied and applied to optical devices. Their small size is expected to play a key role to reduce the operation energy of optical devices, but their sub-wavelength nature hinders sufficient light-matter coupling. Here we show our two approaches to resolve this problem with nanophotonics platforms. The first one is to combine sub-wavelength III/V semiconductor nanowires with Si photonic crystals. We have successfully demonstrated that a high-Q resonator can be formed by placing a nanowire into a slotted photonic crystal. This novel method enables us to create a functional high Q resonator in arbitrary position in Si photonic platform in which strong light-matter coupling is realized [1]. By using technique, we have recently demonstrated lasing oscillation on Si photonic crystals. The second approach is to combine even smaller sub-wavelength III/V nanowires with plasmonic platforms on Si. We successfully placed a III/V nanowire in plasmonic nanoantenna, and observed strong enhancement of light matter interactions. Both methods will expand the possibilities of nanowires and enable us to couple nanowires with in-plane optical waveguides, which will lead to optical circuitry application of sub-wavelength nanowires.

G-1:IL07  MBE Growth of Self Assisted InAs Nanowires on Graphene 
JUNG-HYUN KANG, Y. COHEN, Y. RONEN, M. HEIBLUM, D. CONVERTINO, A. ROSSI, C. COLETTI, S. HEUN, L. SORBA, H. SHTRIKMAN, Braun Center for Submicron Research, Weizmann Institute of Science, Rehovot, Israel; Istituto Nanoscienze-CNR and Scuola Normale Superiore, Italy

The growth of InAs nanowires for various mesoscopic physics experiments has so far drawn much attention thanks to their unique properties. Namely, their high aspect ratio, high electron mobility, the surface pinning in the conduction band, the large spin orbit coupling and high Lande g-factor. These turn them quite suitable for possible observation of the Majorana fermions among many other experiments. InAs nanowires are most successfully grown by gold assisted VLS growth. Nevertheless, replacing the gold droplet with an indium eliminates the potential risk of gold doping along the nanowires which might act as scattering centers degrading the conductance properties. Self-assisted growth of InAs nanowires on Si/SiO2 has been demonstrated by several groups resulting mostly in low aspect ratio nanowires and a highly twinned zinc blende crystal structure. The mixed structure has been attributed to the lack of a liquid droplet at the top of the nanowire, associated with the lower surface tension of the In metal. Graphene has recently been shown to provide an intriguing platform for growth of a variety of III-V semiconductor nanowires. Following work at NTNU1 Norway and by the Fukui group in Japan2 we pursued the self-assisted growth of InAs nanowires on graphene formed by evaporation of Si from SiC. The growth of nanowires on this type of graphene substrate is significantly more easily obtained as compared to growth on Si/SiO2, thanks to the unique long range lattice matching between InAs and graphene. We studied the effect of the nanowires growth parameters such as nucleation conditions, In flux, group V/III ratio and substrate temperature. In particular, we looked into the properties of the high purity graphene layer, namely, a bilayer, a zero/buffer layer or hydrogen-intercalated graphene. We found that the use of the so called zero layer/ buffer layer rather than a complete graphene layer facilitated the growth of much thinner nanowires. We studied the nanowires distribution and morphology by SEM and their crystal structure by TEM which occasionally provides evidence for the presence of an indium droplet at the tip of the nanowires. This together with the small diameters we managed to obtain (40-60 nm) was not as yet sufficient to provide self-assisted growth of nanowires having a pure phase. Instead the wires had a typical mixed wurtzite/zincblende structure with semi periodic regions along the growth direction. Conductance measurements on the self-assisted nanowires at low temperature show a similar behavior to our gold assisted ones. The growth of conducting InAs nanowires on a conducting layer such as graphene opens up new possibilities for electronic and electro optic nanowire devices where the substrate can serve as a global contact/gate.
A.M. Munshi, et al., Nano Lett. 12, 4570-4576 (2012) Y.J. Hong, et al., ACS-Nano 5, 7576-7584 (2011)

G-1:L09  Au-catalyst Assisted Self-assembly of CdTe Nanowires by Metalorganic Vapour Phase Epitaxy
V. DI CARLO, F. MARZO, N. LOVERGINE, Dept. of Engineering for Innovation, University of Salento, Lecce, Italy; P. PRETE, IMM-CMR, Lecce, Italy

CdTe nanowires (NWs) have been proposed as candidates for fabrication of high efficiency photovoltaic cells due to their superior opto-electronic properties in comparison to poly-crystalline thin films. The growth of CdTe NWs well above 450°C has been reported by molecular beam epitaxy, physical vapour deposition, and close-spaced sublimation, using Au as metal-catalyst. No reports have appeared until now on the use of metalorganic vapour phase epitaxy (MOVPE). We demonstrate for the first time the Au-catalyzed growth of CdTe NWs by MOVPE, using diisopropyl-telluride (iPr2Te) and dimethyl-cadmium (Me2Cd) as Te and Cd precursors, on exactly-oriented (111)B-GaAs substrates, which were preliminary deposited with a thick CdTe buffer layer. To suppress CdTe planar growth, a precursor separate-flow process was adopted during NW self-assembly. Vertically-aligned (yield ~99%) CdTe NWs with diameters around 150-230 nm, and heights in the 0.5-1.5 µm range were thus grown above 485°C. Au-rich droplets were found at the tips of each NW, the contact angle to the underlying nanocrystal being ~130°. Furthermore, 7K cathodoluminescence spectra recorded from single NWs showed band-edge emissions typical of zincblend CdTe. We will discuss in details NW growth rate dependence on MOVPE conditions.

G-1:IL11  Guided Growth of Horizontal Nanowires: A General Approach to Structural Control and Large-scale Integration
E. JOSELEVICH, Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel

The large-scale assembly of NWs with controlled orientation on surfaces remains one challenge toward their integration into practical devices. We report the VLS growth of perfectly aligned, millimeter-long, horizontal NWs of GaN [1], ZnO [2], ZnSe [3] and other materials, with controlled crystallographic orientations on different planes of sapphire, SiC [4], quartz [5], and spinel [6]. The growth directions and crystallographic orientation of the NWs are controlled by their epitaxial relationship with the substrate, and by a graphoepitaxial effect that guides their growth along surface steps and grooves. We also demonstrate the massively parallel “self-integration” of NWs into circuits via guided growth [7]. These findings highlight the potential of guided growth as a general approach for the large-scale integration of NWs into a wide range of functional systems.
[1] Science, 333, 1003 (2011). [2] ACS Nano, 6, 6433 (2012). [3] Adv. Mater., 27, 3999 (2015). [4] Nano Lett., 13, 5491 (2013). [5] ACS Nano 8, 2838 (2014). [6] J. Phys. Chem C 118, 19158 (2014). [7] PNAS, 110, 15195 (2013).

G-1:IL12  Quantum Dots in Group IV Nanowires
A. LUGSTEIN1, M. GLASER1, SEBASTIAN GLASSNER1, S. PRUCNAL2, ANDREAS JOHANNES3, SÒNIA CONESA-BOJ4, CARSTEN RONNING3, A. FONTCUBERTA I MORRAL4, W. SKORUPA2, E. BERTAGNOLLI1, 1Institute for Solid State Electronics, Vienna University of Technology, Austria; 2Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany; 3Institute for Solid State Physics, Friedrich-Schiller-University Jena, Germany; 4Lab. des Matériaux Semiconducteurs, EPFL, Lausanne, Switzerland

Monolithically integrated photonic devices on Si are key components in Si-based large-scale integration for future high-performance communication systems. The main obstacles facing towards reliable synthesis of such hybrid systems are related to the difficulties of direct growth of III-V semiconductors on Si. Therefore of particular interest and unique to nanowires is the potential of lateral strain relaxation, mitigating the limitations of material lattice compatibility and allow arbitrarily combined dissimilar materials unattainable in layered structures. We will demonstrate an approach for compound-semiconductor/Si hybrid nanowire synthesis via millisecond range liquid-phase epitaxy regrowth using sequential ion beam implantation and flash-lamp annealing. μ-Raman and photoluminescence spectroscopy was performed on individual nanowires, yielding a spatial mapping of III-V nano crystallites within the Si nanowire. Further it was shown that the manipulation of the Si band structure by exploiting quantum confinement, as well as increasing the transition possibilities within the band structure are promissing approaches to generate light. Thus we will also address the controlled formation of Si and Ge segments, enclosed by two self-aligned contacts enabling hot-carrier devices.

G-1:IL13  III-V Nanowires, Growth Challenges and Applications in Next Generation Photovoltaics

Semiconductor nanowires are filamentary crystals with a diameter in the range between few and few tens(hundred) of nanometers. Their special dimensions and morphology render them extremely interesting for a manifold of applications including electronics, optoelectronics, energy harvesting and biotechnology. In this talk I will discuss the growth of self-catalyzed III-V nanowires on silicon in views of applications in photonics. I will discuss how the silicon should be prepared to obtain a very high yield of vertical nanowires as well as the absorption properties. I will finalize by explaining the advantages of nanowires in solar cell applications along with some new concepts that they enable.

G-1:L15  Selective-area MOVPE Growth of GaAs Nanowires on Silicon using a Non-lithographic Approach to SiO2 Mask Patterning
E. STEVANATO, Dept. of Engineering for Innovation, University of Salento & Italian Institute of Technology, Lecce, Italy; A. PEDIO, F. MARZO, N. LOVERGINE, Dept. of Engineering for Innovation, University of Salento, Lecce, Italy; P. PRETE, IMM-CMR, Lecce, Italy

Catalyst-free growth methods of III-V nanowires (NWs) ensure higher materials purity with respect to Au-catalyst based ones. III-V NW self-assembly by metalorganic vapor phase epitaxy (MOVPE) can be achieved by selective-area (SA) growth using thin SiO2 masks nano-patterned by electron beam lithography (EBL). However, EBL limits the patterned areas to a few hundred squared-microns, and it is time consuming. In this work we present a novel approach to SA-MOVPE growth of GaAs nanowires on (111)Si, which makes use of self-patterned SiO2 masks obtained by liquid phase deposition (LPD). (111)B-oriented GaAs nanoislands were first randomly deposited by MOVPE on (111)Si to serve as nucleation seeds for NWs. As-grown samples were then deposited with a thin (few tens of nm) SiO2 films by LPD. By suitable choice of LPD process conditions, a high degree of selectivity for SiO2 deposition onto Si and GaAs was obtained, leading to a compact SiO2 film onto the bare Si surface and almost no growth on the GaAs nanoislands. As-prepared samples allowed growing perfectly (111)-aligned GaAs NWs by SA-MOVPE on large substrates. We will report on the structure and morphology of as-grown GaAs NWs, and on their growth dependence on fabrication details of self-patterned SiO2 masks and MOVPE parameters.

Session G-2 -  Structure and Properties of 1-D Nanostructures

G-2:IL01  Analysis of 1D-nanostructure Properties using in Situ Transmission Electron Microscopy
D. GOLBERG, WPI-MANA, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan

Nowadays the methods of in situ transmission electron microscopy (TEM) are becoming particularly informative for the explicit analysis of electrical, mechanical, thermal, optical, optoelectronic and photovoltaic properties of diverse nanotubes and nanowires. These methods combine the highest spatial, temporal and energy resolutions peculiar to a high-resolution TEM and unique possibilities of precise manipulations with an individual nanostructure, including its electrical biasing, resistive heating, charging, bending, stretching and illuminating with a light of various wavelengths and pulse frequencies under a continuous control of all electromechanical and optoelectronic parameters. I present our progresses with respect to the detailed analyses of advanced 1D-inorganic nanostructures using various in situ TEM holders. Bending and tensile strength, Young’s modulus of C, B, Si, BN, ZnO, ZnS, CdS and dichalcogenide nanotubes and nanowires, their peculiar deformation kinetics, and thermal, optical and electromechanical properities will be thoroughly discussed.
The author is particularly grateful to Drs. D.M. Tang, Z. Xu, M.S Wang, X.L. Wei, P.M.F.J. Costa, N. Kawamoto, M. Mitome, Y. Bando, C. Zhang, K. Moore and O. Cretu for their key contributions to the in situ TEM works.

G-2:IL02  Thermoelectric Properties of Single Nanowires
I. ZARDO, Department of Physics, University of Basel, Basel, Switzerland

The interest in low dimensional systems has been steadily growing over the last decades. A particularly interesting system is provided by nanowires (NWs). Their functional properties can be manipulated by tuning the crystal structure and by fabricating 3-dimensional complex novel architectures. These unique material features can be exploited to investigate and manipulate lattice dynamic at nanoscale level. Apart from the fundamental interest, these studies can provide new pathways and systems to boost thermoelectricity. The talk will focus on showing our investigations of the thermoelectric properties of semiconductor NWs. We used InAs nanowires to test some of the theoretically predicted effects. We measured the thermal conductivity of wires with diameters ranging from 40nm to 1.5 μm. We demonstrated a reduction of 80% in thermal conductivity for 40nm NWs and we investigated the effect of thermal contact in the most common measurement method for nanoscale thermal conductivity [1]. Furthermore, we show a new method for the complete thermoelectric characterization and figure of merit calculation of single NWs, based on combined spatially resolved μ-Raman spectroscopy and electrical measurements [2].
[1] Nanotechnology 26, 385401 (2015). [2] Accepted in Nano Research.

G-2:IL03  X-ray Investigations of Single Nanowire Devices
J. WALLENTIN, Synchrotron Radiation Research, Lund University, Sweden

The long absorption lengths of hard X-rays make them uniquely suitable for in operando investigations, and recent advances in the focusing of hard X-rays open up the possibility to investigate functional nanodevices. We have developed methods for characterizing single nanodevices with hard X-rays, while simultaneously performing electrical measurements. In these investigations, we use electrical bias as a stimulus and the X-ray as a probe, or vice versa. Both X-ray diffraction and X-ray imaging can be performed. Scanning XRD was performed along the axis of a single nanowire transistor. The measurements give the direction and strain of the entire single crystal nanowire, also in regions covered by the metal contacts. In the as-processed device, we found that the strain was small but that the nanowire was bent in an arch between the contacts. Since the measurements were non-destructive, bias voltage could be supplied. The arch gradually disappeared at high voltages, while the lattice constant changed in the contact regions correlated with a reduction in electrical conductance. Measurements with another nanowire device show that the X-rays increased the electrical conductance by five orders of magnitude.

G-2:IL04  From 1D Silicene Nanoribbons to 2D Sheets
P. DE PADOVA, Consiglio Nazionale delle Ricerche, Istituto di Struttura della Materia, Roma, Italy

The synthesis of monolayer silicene, a single layer of silicon atoms densely packed in a honeycomb graphene-like structure, has generated very strong interest [1-3]. This new allotrope of silicon, arranged in a sp2/sp3-like configuration [4], both for one-dimensional (1D) nano-ribbons (SiNRs) with a very high aspect ratio [4] and 2D silicene sheet [1], including their multilayers, [5, 6] still present many exciting promises due, typically to its Dirac fermions [6, 7] and its direct compatibility with current silicon based electronics, although at present there is a scientific debate that stimulates different interpretation.
[1] P. Vogt, P. De Padova, et al., Phys. Rev. Lett. 108, 155501-5 (2012). [2] C.-L. Lin, et al., Appl. Phys. Exp., 5, 045802-3 (2012). [3] A. Fleurence, et al., Phys. Rev. Lett. 108, 245501-5 (2012). [4] P. De Padova et al., Appl. Phys. Lett., 2011, 98 081909;[5] P. De Padova, et al., Nano Lett., 12, 5500 (2012). [6] P. De Padova et al., J. Phys.: Condens. Matter, Fast Track Comm. 25, 382202 (2013); P. Vogt et al., Appl. Phys. Lett. 104, 021602-1-5 (2014); E. Salomon et al., J. Phys.: Condens. Matter, 7, 185003 (2014). [7] P. De Padova et al., Appl. Phys. Lett., 96, 26190, (2010);[8] P. De Padova et al., 2D Materials 1, 021003 (2014).

G-2:IL05  Dislocation-driven Nanowire Growth and Lead Halide Perovskite Nanowire Lasers with Low Lasing Thresholds and High Quality Factors
SONG JIN, Department of Chemistry, University of Wisconsin-Madison, Madison, WI, USA

I will first discuss a general growth mechanism of nanowires, in which screw dislocation defects provide the self-perpetuating steps to enable anisotropic crystal growth in one-dimensional nanowires, nanotubes, two-dimensional (2D) plates, and other multi-dimensional morphologies. Particularly, we used such insights to understand the crystal growth of lead halide perovskite solar materials and developed the solution growth of single crystal nanowires, nanorods, and nanoplates of methylammonium and formamidinium lead halide and other perovskites via a dissolution-recrystallization pathway. The long carrier lifetimes and low non-radiative recombination rates that enable the remarkable performance of perovskites in solar cells also make them ideal for semiconductor lasers. We show room temperature and wavelength tunable lasing from these perovskite nanowires with the lowest lasing thresholds and highest quality factors ( ~ 3600) reported to date for semiconductor nanowire lasers with nearly 100% lasing quantum yields. Such lasing performance, coupled with facile solution growth of single crystal nanowires and broad tunability of emission color makes perovskite nanostructures ideal for nano-photonic and optoelectronic devices, in parallel with their development in solar cells.

G-2:IL06  Contact-free Surface Acoustic Wave Control of Nanowire Heterostructures
H.J. KRENNER1, M. WEIß1, J.B. KINZEL1, F.J.R. SCHÜLEIN1, M. HEIGL1, D. BÜHLER1, A. WIXFORTH1, D. RUDOLPH2, M. BICHLER2, G. ABSTREITER2,3, J.J. FINLEY2, G. KOBLMÜLLER2, 1Lehrstuhl für Experimentalphysik 1, Universität Augsburg, Augsburg, Germany; 2Walter Schottky Insitut, TU München, Garching, Germany; 3Institute for Advanced Study, TU München, Garching, Germany

Radio frequency control of nanostructures lies at the forefront of contemporary nanoscale research. Towards this challenging goal, surface acoustic waves (SAWs) provide a particularly versatile tool to manipulate and probe a broad variety of nanosystems. These “nanoquakes on a chip” promise massively parallel manipulation via acousto-mechanical and acousto-electric couplings. We demonstrate that the strain and the large piezoelectric fields accompanying the SAW dynamically control the optical emission characteristics of GaAs-(Al)GaAs core-multi-shell heterostructure nanowires (NWs). The acousto-electric coupling leads to pronounced dynamic suppression of the NW’s optical emission on a nanosecond timescale [1] by SAW-driven spatio-temporal carrier dynamics. We study this effect on single nanowires and determine the mobility of both electrons and holes in the native material limit [2]. Moreover, dynamic control spectral and occupancy state control of single quantum dot-like emission centers is demonstrated at radio frequencies [3,4].
[1] J.B. Kinzel et al., Nano Lett. 11, 1512 (2011). [2] J.B. Kinzel et al. submitted (2015). [3] M. Weiß et al., J. Phys. D: Appl. Phys. 47, 394011 (2014). [4] M. Weiß et al., Nano Lett. 14, 2256 (2014)

G-2:IL07  GaAs-AlGaAs Core-(Multi)Shell Nanowire Structures: MOVPE Growth and Nano-scale Optical/Electronic Properties
P. PRETE, IMM-CNR, Lecce, Italy; R. ROSATO, E. STEVANATO, F. MARZO, N. LOVERGINE, Dept. of Engineering for Innovation, University of Salento, Lecce, Italy

III-V compounds nanowires (NWs) have gathered considerable research interests in recent years. Radial modulation of NW composition in the form of core-(multi)shell heterostructures promises to impact several nano-device technology fields by adding novel degrees of freedom to the design of NW-based devices. We report on the Au-catalyzed metalorganic vapor phase epitaxy growth and nano-scale optical characterization of GaAs-AlGaAs core-shell and core-multishell NW structures. The radiative emission of as-grown structures was studied by low-temperature cathodoluminescence (CL) spectroscopy and high spatial resolution imaging performed on single NWs. By comparing CL results with photoluminescence (PL) spectra collected from dense NW arrays, we consistently demonstrate the combined effect of strain-induced band-shift and axial piezo-fields inside the material, as the origin of previously reported red-shifts of GaAs exciton emission in core-shell NWs. Insertion of a few nanometres thin GaAs shell in between two AlGaAs shells overgrown around the NW GaAs core lead to the formation of so-called quantum well tubes (QWTs). CL imaging of QWTs allowed to spatially resolving different contributions found in the CL and PL spectra, ascribed to inhomogeneities of the QWT thickness along the NWs.

G-2:IL09  Structure-property Correlations in 1D-nanowires using Atom Probe Tomography
L.J. LAUHON, Dept. of Materials Science and Engineering, Northwestern University, Evanston, IL, USA

Microscopy plays a central role in the advancement of nanoscience and nanotechnology by enabling the direct visualization of nanoscale structure, and by extension predictive models of novel physical behaviors. Correlated imaging of nanoscale structure and properties is an important frontier that can provide a rational basis for the engineering of new materials to meet challenges in energy, sustainability, medicine, and information technologies. Semiconductor nanowires are candidates to realize the next generation of efficient light emitting diodes and solar cells, and a fundamental understanding of their structure property relationships is essential to gauging and maximizing their potential. We have used atom probe tomography to visualize the distribution of atoms in three dimensions with nanoscale resolution, providing new insights into growth mechanisms and the resulting the distribution of dopant atoms. Correlated 3D characterization and modeling of III-V semiconducting nanowire heterostructures reveals how the confinement of electrons and photons is influenced by size, shape, and interfaces.

G-2:IL10  Quantum Gases in ZnO Nanowires
R. SCHMIDT-GRUND, Universität Leipzig, Institut für Experimentelle Physik II, Leipzig, Germany

I will discuss different regimes of light-matter interaction in ZnO-based nano- and micro-wire cavities of various types. Depending on the photonic confinement and exciton-photon interaction strength, the microcavities are either in the weak or strong coupling regime providing coherent photon or exciton-polariton systems, respectively. Different types of lasing arise, gained by electron-hole plasma [1], doubly stimulated phonon-photon emission [2], and from Bose-Einstein condensates of exciton-polaritons [3]. The 1D-geometry of the wires promotes long-distance transport of these bosonic quantum gases and their multi-mode structure enables effects like parametric mixing. The photonic confinement is usually provided by reflections at the wires end- or by total internal reflection at the side-facets, resulting in Fabry-Perot (FP) and/or whispering gallery (WG) type modes. By lateral coating of opposite or of all side-facets with distributed Bragg reflectors, very complex WG-FP-mixed-type modes are obtained. This, among others, allows for the coexistence of the weak and strong coupling regime which we could confirm by mode-simulations.
[1] C. Czekalla et al, pss b 247, 1282 (2010). [2] T. Michalsky et al, APL 105, 211106 (2014). [3] C.P. Dietrich et al, PRB 91, 041202(R) (2015).

G-2:L13  Unraveling Size Effect of Metallic Nanowires towards Ultra-strong Metal Nanostructured Material
IN-SUK CHOI, High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul, Rep.of Korea

The mechanical properties of metallic nanowires have systematically been investigated to understand the size effect of nanomaterials. In this presentation, we demonstrate the size effect of single crystalline FCC noble metallic nanowires. We illustrate how surface effects enable the strong and ductile behavior by experimentally applying tensile deformation to rhombic cross section Au, Pd and AuPd nanowires that have a <110> orientation and four bounding {111} transverse surfaces. Interestingly, the high ductility, and fracture strains of about 50% are obtained through a geometric reorientation of the cross section from rhombic to square through long-ranged, coherent twin propagation. Importantly, the ductility is not reduced with an increase in strength, where both the nanowire yield and twin propagation stresses increase with decreasing nanowire diameter. We also demonstrate the size effect of multilayered Ni based nanowires. Beyond reducing diameter of NWs to enhance strength, we introduce a Ni multilayer nanostructure providing Ni NWs with superior strength, even with diameters exceeding 200 nm by using micro-alloying technique. The carefully controlled multilayered Ni nanowires exhibit unprecedentedly high tensile strength by decreasing layer thickness.

Session G-3 - Modeling and Simulation of 1-D Nanostructures

G-3:IL01  Electronic Transport in 1D Nanostructures
J. LI, Y.M. NIQUET, Univ. Grenoble Alpes & CEA Grenoble, France; C. DELERUE, IEMN, Lille, France

We review recent theoretical and modeling works on electronic transport in 1D semiconductor (Si, Ge) nanostructures. We calculate the phonon-limited mobility of electrons and holes using a fully atomistic approach, by combining tight-binding calculations for electronic states and valence-force field description of the phonons. All electron-phonon processes are considered in the simulations, and the electron-phonon couplings are directly derived from the calculations without any experimental input. We summarize different results obtained during the last years: 1. Carrier mobility in pristine Si and Ge nanowires, effects of the quantum confinement. 2. Effects of strains on the carrier mobility. 3. Transport in Si/Ge core-shell nanowires. 4. High-field transport in Si nanowires. 5. Comparison between 1D (nanowire) and 2D (layer) Si nanostructures.

G-3:IL02  Theoretical Study of Ordered III-V Nanowire Arrays for Light Emission and Detection
B. WITZIGMANN, University of Kassel, Kassel, Germany

In this presentation, the physical principles of semiconductor nanowire arrays are discussed, with a focus on photovoltaics and solid state lighting. As analysis tools, specific physics-based numerical models for nanophotonics and -electronics have been developed. In particular, the three-dimensional nature of a wire array, including the substrate and the free space on top is included in the study. For the optical extraction efficiency of an LED, absorption of electromagnetic energy in the contacts and the active layers themselves, as well as re-emission are investigated. The latter is an effect that couples the electronic and the optical system. In addition, the optical density of states is analyzed and its impact on the extraction efficiency is shown. Finally, the total electro-optical efficiency of a nanowire array LED is presented and compared to state of the art thin-film LEDs. For the nanowire array solar cell, an electromagnetic and electronic analysis is presented, from which fundamentals in terms of materials choice and wire geometry will be derived. It shows that regular III-V nanowire arrays can reach absoabsorptivities identical to bulk, with the advantage of substrate flexibility, low material consumption, and improved strain engineering for multi-junction cells.

G-3:L04  Influence of the Arsenic Flux on the Formation of Axial Heterostucture in (Al,Ga,In)As Nanowires
N. SIBIREV1,2, A. KORYAKIN1, V. DUBROVSKII1,2, 1Saint-Petersburg Academic University, ITMO University, Russian Federation; 2Saint-Petersburg State University, Russian Federation

Semiconductor heterostructure nanowires (NW) are one of the most promising building blocks for various nanoelectronic devices. NWs are usually grown via the so-called vapor-liquid-solid mechanism on the surfaces activated by the droplets of a catalyst (e.g., Au). Here we theoretically studied the formation of heterostructures in ternary (Al,Ga,In)As nanowires grown with or without a foreign catalyst. Our approach is based on determining the chemical potential of a multi-component liquid using the regular solution model and Stringfellow’s scheme. We assume that the NW growth rate is determined by the nucleation of islands. Yet the composition of a given NW monolayer (ML) is defined during the lateral growth of these islands. Indeed, islands emerge as a cluster of several atoms and later they extend laterally to fill the complete ML slice. Our model allows explaining asymmetry of leading and trailing heterointerfaces. Two possible reasons of content oscillations near heterointerface are described. The first one comes from elastic stress near the interface, and another one is the result of distinct Al,Ga,In solubility. The dependence of ternary (Al,Ga,In)As NW composition on As flux is found. The surprising influence of the As flux on (Al,Ga,In)As NW composition is explained.

Session G-4 -  Processing, Characterization and Modeling of 1-D Nanostructure-polymer/metal/ceramics Composites

G-4:IL01  Selective Lateral 1D Epitaxy: III-V Planar Nanowire Growth, Doping, and Transistors
XIULING LI, Department of Electrical and Computer Engineering, Micro and Nanotechnology Laboratory, University of Illinois, Urbana, IL, USA

III-V compound semiconductor, due to its high mobility and versatile heterojunctions, is considered as one of the highly promising candidates for beyond-silicon high speed low power RF and logic applications. Nanowires (NWs) with their inherent 3D cross-sections can greatly reduce the short channel effects that limit the scalability and linearity of various type of transistors. Generally, vertical array-based III-V nanowire transistors have been the focus because of the preferred nanowire growth direction by the vapor-liquid-solid (VLS) method. However, the out-of-plane <111> orientation is highly susceptible to stacking faults formation; the high aspect ratio geometry makes processing challenging; and prevents high-speed operation because of the severe inherent parasitic capacitance among other. To address these issues, we have developed a selective lateral 1D epitaxy (SLE) method using MOCVD, where the NWs self-assemble along certain crystal directions in plane with the substrate surface, instead of from the substrate up [1,2,3]. The NWs grow out of Au nanoparticles seeds only, thus the selectivity, via the VLS mechanism. By patterning the Au nanoparticles, site-controlled perfectly parallel arrays of planar NWs can be formed. Their planar and self-aligned nature makes these in-plane NWs completely compatible with large scale manufacturing of NW-based integrated nanoelectronics. Here we present the SLE growth mechanism, doping characterization, and the electrical performance of various devices including GaAs/AlGaAs HEMTs [3, 4] and InAs nanowire gate-all-around MOSFETs [5].
[1] S.A. Fortuna, J. Wen, I.S. Chun, and X. Li, Nano Lett. 8, 4421-4427 (2008). [2] C. Zhang, X. Miao, P. K. Mohseni, W. Choi, and X. Li, Nano Lett. 14, 6836–6841 (2014). [3] X. Miao, K. D. Chabak, C. Zhang, P. K. Mohseni, D. E. Walker Jr., and X. Li, Nano Lett. 15, 2780-2786 (2015). [4] K. D. Chabak, X. Miao, C. Zhang, D. E. Walker Jr., P. K. Mohseni, and X. Li, "RF Performance of Planar III-V Nanowire-Array Transistors Grown by Vapor-Liquid-Solid Epitaxy," IEEE Electron Device Lett. 36(5), 445-447 (2015). [5] C. Zhang, W. Choi, P. Mohseni, and X. Li, "InAs Planar Nanowire Gate-All-Around MOSFETs on GaAs Substrates by Selective Lateral Epitaxy," IEEE Electron Dev. Lett., 36(7), 663-665 (2015).

G-4:L04  Biodegradable Inorganic Nano-architectures to avoid Accumulation in Excretory System Organs
D. CASSANO1,2, D. ROTA MARTIR1, G. SIGNORE1, V. PIAZZA1, V. VOLIANI1, 1Center for Nanotechnology Innovation @NEST, Istituto Italiano di Tecnologia, Pisa, Italy; 2NEST-Scuola Normale Superiore, Pisa, Italy

One of the major concerns regarding the clinical translation of metal nanoparticles is related to the question of persistence in organisms. The dilemma in the choice of particle size needed for clinical applications versus efficient body clearance has created a serious conflict in nanotechnology. In order to overcome these issues we have recently introduced a versatile nanosystem composed by: i) arrays of 3 nm gold nanoparticles, ii) functionalizable FDA-approved commercial polymers surrounding the gold nanoparticles, and iii) biodegradable and derivatizable silica shell embedding the polymer-nanoparticle assembly. These robust nanocapsules maintain the intriguing features of gold nanospheres but are biodegraded to their building blocks in few hours in cellular environment, potentially overcoming the issue of accumulation thanks to the renal clearance of these components. The last achievements on cellular and in vivo experiments resulted from this novel approach will be discussed together with the therapeutic and imaging applications, among which chemo/radio-therapy and photoacoustic.

G-4:L05  Boron Nitride Nanotube: Synthesis, Functionalization, and Nanocomposites
C.M. HOMENICK, Y. MARTINEZ-RUBI, K.S. KIM, M.B. JAKUBINEK, C.T. KINGSTON, B. SIMARD, Security and Disruptive Technologies Portfolio, National Research Council Canada, Ottawa, Canada; B. ASHRAFI, Aerospace Portfolio, National Research Council Canada, Montreal, Canada

Boron nitride nanotubes (BNNTs) are analogous to carbon nanotubes (CNTs) with respect to their low density, high aspect ratio, strength, stiffness, and thermal conductivity. However, they distinguish themselves from CNTs with their high thermal stability, wide band gap, high neutron absorption, piezoelectric effect, and lack of absorption in the visible spectrum. Chemical modification of the nanotube surface is essential to enhance dispersion and processability, and translate these properties to useful composites. Herein, we introduce our pilot-scale metal catalyst free BNNT synthesis that has addressed supply limitations and enabled the production of macroscopic assemblies such as fibers and sheets. Subsequently, we discuss approaches for surface functionalization of BNNTs and BNNT assemblies, which facilitate processability, and the development of BNNT composites with improved mechanical and thermal properties.

G-4:L06  Fabrication of Y2Ti2O7/SiC Functionally Graded Materials by Magnetic Field Application
S.T. NGUYEN, T. NAKAYAMA, H. SUEMATSU, T. SUZUKI, S. TANAKA, Y. NAGASAWA, K. NIIHARA, Nagaoka University of Technology, Nagaoka, Niigata, Japan

SiC/SiC ceramic matrix composites is the most promising materials for the next generation of gas turbine engines blades. Unfortunately, SiC is very weak against water vapor in hydrocarbon combustion environments, and hence must be protected by environmental barrier coatings (EBC). Aiming to improve the performance of such EBC, this research has focused on the structure of coating layers. Functionally graded materials (FGM) of SiC in Y2Ti2O7 matrix is proposed to lessen the effect of thermal expansion mismatch between the coating and the substrate during operation, which cause delamination of the EBC. In order to control the arrangement of SiC nanofibers in magnetic field, we coated nickel (Ni) nanoparticles on their surface using solution chemistry routes. The Ni/SiC nanofibers were added into Y2Ti2O7 slurry, which had been prepared by ball-milling Y2Ti2O7 powder with polyethyleneimine dispersant in 2-propanol solvent, then was dispersed by sonication. The slurry was then cast into a polyethylene mold and subjected to a magnetic field. After consolidation, the green body was pressureless sintered in argon atmosphere. X-ray computed tomography confirmed that Ni/SiC nanofibers were aligned along the magnetic field direction and gradient structures were successfully configured.

Session G-5 -  1-D Nanostructures-based Applications

G-5:L02  Gallium Arsenide Nanowire Lasers               
C. JAGADISH, Department of Electronic Materials Engineering, Research School of Physics and Engineering, Australian National University, Canberra, A.C.T., Australia

GaAs is the most studied and used III-V semiconductor material in planar configuration. Its applications, however, have been limited in nanowire configuration because of very large surface recombination velocity (~106 cm/s). Large surface recombination velocity in conjunction with large free surface in GaAs nanowires results in surface assisted non-radiative recombination process being the dominant recombination process. This degrades the radiative efficiency of GaAs nanowires, limiting its optoelectronic applications. In my presentation, I will discuss three approaches to combat the surface states assisted non-radiative recombination processes: (i) surface passivation, (ii) doping and (iii) quantum confinement. I will quantify the radiative efficiency of GaAs nanowires that employ above strategies and more importantly, present results demonstrating room-temperature lasing behavior in these nanowires to highlight the potential of these approaches.

G-5:IL03  Artificial Photosynthesis on Metal-nitride Nanowire Arrays              
ZETIAN MI, Md G. KIBRIA, B. ALOTAIBI, S. FAN, Y. WANG, S. VANKA, Department of Electrical and Computer Engineering, McGill University, Montreal, Quebec, Canada

High efficiency artificial photosynthesis, that can convert solar energy directly into chemical fuels, has been extensively investigated. Critical to this development is the stable and efficient generation of hydrogen from water under direct sunlight irradiation. To date, however, success in finding abundant visible-light active photocatalyst has been very limited. Recently, metal-nitrides have attracted considerable attention for applications in artificial photosynthesis, due to their extraordinary stability and tunable energy bandgap across nearly the entire solar spectrum. Moreover, III-nitrides are the only known material whose energy bandgap can straddle the redox potential of water under deep visible and near-infrared light irradiation. In this context, we have investigated the design, fabrication, and performance characterization of multi-band InGaN/GaN nanowire photoelectrodes. InGaN/GaN core/shell nanowire arrays on Si can function as a double band photoanode in acidic solution, and relatively high incident-photon-to-current-conversion efficiency (up to 37%) is measured under ultraviolet and visible light irradiation. Moreover, by exploiting the lateral carrier extraction scheme of 1-dimensional nanowire structures, we have developed an adaptive PV-PEC photocathode, consisting of monolithically integrated GaN/p-InGaN nanowire arrays on a planar Si solar cell wafer, that can surpass the current matching requirements of conventional tandem electrode. An applied bias photon-to-current efficiency of 8.7% is measured. With the incorporation of Cu co-catalyst, we have also measured the direct conversion of CO2 into CH4 and CO. At -1.4 V vs Ag/AgCl, the Faradaic efficiency can reach ~19 % for the 8e- photoreduction to CH4, which is more than 30 times higher than that for the 2e- reduced CO (~0.6%). The nanowire/Si solar cell photocathode also showed excellent stability towards CO2 reduction.

G-5:IL05  Nanowire Field-effect Transistor-based Biosensors: A Tool for Life Science
YIT-SONG CHEN, Department of Chemistry, National Taiwan University, Taipei, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan

Silicon nanowire field-effect transistors (SiNW-FETs) have been used as a highly sensitive biosensor in biomedical diagnosis and cellular recording investigations (Nano Today, 6, 131-154 (2011)). We have applied reusable SiNW-FETs for detecting neurotransmitters release from living neurons, protein-protein interactions (PNAS, 107, 1047-1052 (2010)), K+ efflux from live cells, and protein-microRNA interactions. We also developed aptamer-modified multiple-parallel-connected (MPC) SiNW-FETs for sensitive detection of specific targets (e.g., dopamine, K+, neuropeptide Y, etc.). As an example, this MPC SiNW-FET was applied to monitor the dopamine release from living PC12 cells under hypoxic stimulation (JACS, 135, 16034-16037 (2013)). We resolved the controversial pathways that the increase in intracellular Ca2+ to trigger dopamine secretion from PC12 cells is dominated by an extracellular Ca2+ influx, rather than the release of intracellular Ca2+ stores. In addition, we applied 2D materials (e.g., graphene and layered semiconductors)-based FETs for the detection of membrane protein interactions. These 1D and 2D bio-nano-electronic FET devices, which are capable of integrating with living cell systems, provide a promising tool for disease diagnosis and cellular investigations.

Poster Presentation

G:P01  Effect of Buffer Layer on Electrical and Optical Properties based on SnO2/Ag/SnO2 Multi Layer Film
JIN-GYUN KIM, GUN-EIK JANG, Department of Materials Engineering, Chungbuk National University, Cheongju, Korea

The hybrid structure SnO2/Ag/Nb2O5/SiO2/SnO2 was prepared on glass substrates by sequential RF/DC magnetron sputtering at room temperature. The electrical and optical properties of hybrid multi-layer film were systematically investigated by inserting Nb2O5 and SiO2 layer between SnO2/Ag /SnO2 layers. .In order to estimate and compare with the experimental results, the simulation program, EMP (Essential Macleod Program) was adopted. The X-ray diffraction patterns of the prepared SnO2 multi-layered films were found to have a typical amorphous state due to low substrate temperature. Measured film thickness was about 100 nm. Especially SnO2 (45nm) /Ag (10nm) /Nb2O 5(10nm) /SiO2 (10nm)/SnO2 (25nm) film exhibits a sheet resistance of 6.3 Ω/sq with an optical transmittance of 84% in visible region. The surface roughness maintained a relatively small range about 4nm.

G:P02  Highly Flexible and Transparent Conductive Electrode based on Silver Nanowires
CHANG SU KIM, MYUNGKWAN SONG, DONG-HO KIM, Advanced Functional Thin Films Department, Korea Institute of Materials Science (KIMS), Changwon, Korea

Transparent electrodes have been widely used in electronic devices such as solar cells, displays, and touch screens. Highly flexible transparent electrodes are especially desired for the development of next generation flexible electronic devices. Although indium tin oxide (ITO) is the most commonly used material for the fabrication of transparent electrodes, its brittleness and growing cost limit its utility for flexible electronic devices. Therefore, the need for new transparent conductive materials with superior mechanical properties is clear and urgent. Ag nanowire (AgNW) has been attracting increasing attention because of its effective combination of electrical and optical properties. However, it still suffers from several drawbacks, including large surface roughness, instability against oxidation and moisture, and poor adhesion to substrates. These issues need to be addressed before wide spread use of metallic NW as transparent electrodes can be realized. In this study, we demonstrated the fabrication of a flexible transparent electrode with superior mechanical, electrical and optical properties by embedding a AgNW film into a transparent polymer matrix.

Cimtec 2016

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